Generally speaking, difficulties in repairing manifolds arise from the inability to adequately secure manifolds in place, center and align manifolds during machining, and adapt manifold holding tools to accommodate resurfacing equipment from diverse manufacturers. Since “V” block designed engines were introduced to the general automotive consumer in the 1930's and 40's, dedicated tooling at the Original Equipment Manufacturer (OEM) level has been required to create precision intake and exhaust manifolds having very specific angle and size limitations. This specialized tooling has typically been unavailable to the average automotive rebuilder. Thus, manifolds having reparable damage in the form of corrosion, cracks, and warp are often discarded because remachining those manifolds to original specification is exceedingly difficult without manufacturer specific tooling. Even in circumstances where specialized tooling is available, the variety and type of manifolds generally encountered by the typical automotive rebuilder renders any type of specialized tooling of limited utility: modifying OEM tooling to accommodate various OEM manifolds is nearly impossible.
Prior Approaches
Because accurately machining a manifold is so difficult, many shops have adopted questionable practices to compensate for their inability to precisely machine damaged manifolds. For example, some shops cut the cylinder head's manifold mounting face to compensate for material that should have more properly been removed from the manifold mounting face itself. This practice creates heads that are no longer standard and therefore not freely interchangeable within their customary applications. Other shops drill oversized intake manifold bolt holes so that the intake manifold appears to fit the engine block properly while in fact it does not. This practice often results in hidden problems—e.g. port misalignment, vacuum leaks, and fluid leaks. Still other shops sell replacement manifolds rather than attempt difficult repairs that, given the proper tooling, would otherwise be cost effective to repair. Finally, some shops, attempting to overcome the lack of tooling, use abrasive belts to machine manifolds. Although manifolds machined with abrasive belts have the appearance of precision machining, the opposite is true because the machinist cannot retain adequate control over the machining process.
Finally a costly practice in the automotive repair industry is modifying manifolds for use with performance engines. Often performance shops create modified engine blocks and cylinder heads that cannot accommodate OEM manifolds. Machining manifolds to match custom blocks and heads requires a high degree of skill and precision causing a completed performance engine's price to be substantially higher than conventional repair and machining.
These practices combine to cause more problems than they solve resulting in poorly machined manifolds and inadequately repaired engines.